Forum Discussion
Phantom Office 365 Mailboxes
By any chance, do these accounts use the Outlook for iOS or Outlook for Android clients? If so (as explained in https://www.petri.com/outlook-ios-android-dumping-aws-q3), this might be evidence of the mailbox cache maintained within Office 365 to allow mailbox data to be processed and then synchronized to those clients. The users should not see the phantom mailboxes, so that is a bug... But can anyone confirm the theory?
Thanks for calling that out Tony, I hadn't read that in the past and it's a good primer for what I'm working on to get Outlook mobile as the "standard".
In this case though, the users are not using Outlook on either iOS or Android and I know they've factually never tried to get in that way.
I just got off the phone with support and they seem to be curious about this one too. Maybe the PG is having some fun with us again. ;) Either way it's feeling more and more like a bug.
Just thinking, does any information exist in the phantom mailboxes?
It doesn't appear that way - but I can generate new content within it. Contacts, sent items, calendar invites, etc. Presents an interesting compliance issue since technically I can't discover the content if it starts there.
I had a conversation with the Outlook team and the phantoms are not their responsibility. Stranger forces are at work!
Well, we've engaged the other grumpies to test on this and so far no one has been able to reproduce it. I should also be able to give it a go tomorrow. Ingo Gegenwarth suggested that you should check the headers from OWA, as they might reveal some more info. For example, there should be a heder named "X-UPNAnchorMailbox" listing the actual UPN of the user object.
Do tell us what you dig up with support, it's kinda hard to troubleshoot issues like these on a public forum where you cannot share the needed details.
I dug through the headers and I'm not seeing X-UPNAnchor or anything of that sort...
I forgot to mention earlier that these are on-prem AD mailusers that are synched to Office 365 via AADConnect. (might be relevant)
What's more interesting here:
Mail user target address: JTest@tenant2.com
OWA shows logged in user: JTest@tenant1.com
Email that arrives comes from MailUser Target Address of jtest@tenant2.com. This means that it's actually allowing me to send out of tenant1 as a domain that isn't even registered. Bizarre (yeah, my head is spinning)
I'll report back our the end resolution or more details as they come.
